My greenhouse is fragrant with the scent of coriander at the moment. Each time I open the door a waft of spicy, peppery perfume drifts out on the warmed air from the long trough of young plants parked just inside, waiting for the frosts to pass so they can move to just outside my back door.
But though they smell lovely, I noticed yesterday as I was watering that all is not well with them. Some are growing away lustily with bushels of fresh green leaves: but others are twisted and stunted, the leaves folded in on each other and in some cases a little wilted.
It wasn’t hard to find the culprit. Turn the leaves over, and there they are: little diaphanous green flies crouched almost invisible against the underside of the leaf. Another giveaway was the little army of ants marching all over trough, compost and plants: they love the honeydew the aphids excrete and ‘farm’ the greenfly, defending them from predators, so if you’ve got ants wandering over your plants you can be fairly sure you’ve got greenfly.
Anyone who grows roses will tell you all about greenfly, but they’re even more of a pain in the neck for the veg grower whose aim is to eat the veg before the greenfly do. Greenfly infest annual herbs like coriander, basil and occasionally parsley. They’ll crawl their way around your spinach and chard, and occasionally take up residence among seedling beetroot. Peas, beans, cucumbers, tomatoes – actually there’s not much they don’t attack.
You should always take greenfly seriously, as not only do they stunt your plants, they can also carry viruses from one plant to another. For cucumbers, courgettes and melons that’s instant death, as viruses are incurable. So those little flies can potentially have an impact out of all proportion to their size.
You’ll never get rid of greenfly altogether: not without releasing chemical armageddon on them, anyway, and personally I’d rather eat veg chewed by greenfly. If they haven’t reached plague proportions, it’s feasible to keep them under control and limit the damage just by squishing them off: every morning, just rub the growing tips of each plant gently between thumb and forefinger and try not to shudder too much (it really is a horrible job as the ends of your fingers turn mushy green with… OK I won’t go on).
I’m having a bit of trouble doing that with my little coriander plants, though, as coriander has thin, delicate leaves and when they’re young they’re little more than tissue-paper. So I’m doing more damage to them by rubbing them than I would leaving the greenfly there.
So I’m bringing forward my plans to look into insecticidal soap sprays. I’d already decided to start using these this year on the kale and cabbages, which last year had a nasty attack of mealy cabbage aphid: but the same stuff works on ordinary greenfly. I’m not sure I much fancy eating coriander coated in soap, but I shall just use it while the plants are little to get them past this tricky stage. Then by the time they’re grown big and beefy a little greenfly won’t bother them as much. Here’s hoping….
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